1. Field of the Invention
This invention relates to cryosurgical probes and more particularly to a cryoablation probe with enhanced flexibility under conditions of near critical nitrogen.
2. Description of the Related Art
Cryoablation probes (“Cryoprobes”) are used to treat a variety of diseases. Cryoablation probes quickly freeze body tissue, causing the tissue to die after which it will be absorbed by the body, expelled by the body, sloughed off or replaced by scar tissue. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors including breast cancer, cancerous tumors of the liver, lung, kidney, soft tissues, as well as glaucoma and other eye diseases. Cryoablation may also be used for the treatment of a number of other diseases and conditions including the treatment of cardiac arrhythmias, such as atrial fibrillation. In addition, endovascular and endoscopic uses of cryotherapy are emerging for vascular and cancerous conditions.
During open surgeries, any suitable cryoprobe with enhanced flexibility may used to greater assist destruction of any undesirable tissue. Currently, open surgery for cancer is limited by stiff metal probes, or needles, which have limited their placement into the tumor, or can only be placed on the tumor surface with a disc-like applicator. A suitable probe that could conform to a surgeon's hand, or other operative equipment, would greatly expand tumor access and cryoablation applications. For chest surgery, transmural cryo-lesions can be created on or in the heart to treat cardiac arrhythmia (including atrial fibrillation). A suitable cryoprobe would be useful for this application. Due to the nature of the procedure and anatomical locations that lesions must be placed, the cryoprobe must be sufficiently flexible by the surgeon to be placed on the correct location of the heart surface.
Although a rigid probe can be provided with a predetermined shape, one must select a probe that has the most appropriate shape for positioning the working portion of the probe in contact with the treatment site in view of the particular anatomical pathway to be followed in the patient. It will be appreciated that a large inventory of rigid probes may be required to accommodate the various treatment sites and patient anatomies. Further, for a patient having a relatively uncommon anatomic configuration and/or a difficult to reach treatment site, all rigid probes of an existing set may have less than optimal shapes for positioning. This may impair the prospects of successfully carrying out the treatment procedure, especially when the treatment is one such as an ablation treatment that relies on good tissue contact and operates locally upon the contacted tissue. For an ablation probe which must bear against tissue at the remote region to ablate a lesion, the contour followed by the probe in reaching the target site will in general further restrict the direction and magnitude of the movement and forces which may be applied or exerted on the working portion of the device to effect tissue contact and treatment.
The prior art includes references to malleable and flexible cryoprobes. For example, U.S. Pat. No. 6,161,543, issued to Cox et al, discloses the use of a malleable probe. The probe has a malleable shaft. A malleable metal rod is coextruded with a polymer to form the shaft. The rod permits the user to shape the shaft as necessary so that a tip can reach the tissue to be ablated.
U.S. Pat. No. 5,108,390, issued to Potocky et al, discloses a highly flexible cryoprobe that can be passed through a blood vessel and into the heart without external guidance other than the blood vessel itself.
Several patents disclose the use of bellows-type assemblies for use with cryoablation systems. For example, U.S. Pat. No. 6,241,722, issued to Dobak et al, discloses a cryogenic catheter with a bellows and which utilizes a longitudinally movable Joule-Thomson nozzle of expansion. The Dobak '722 device preferably uses closed media-flow pathways for efficient recycling of the media employed.
Dobak et al, in U.S. Pat. No. 5,957,963, disclose the used of a flexible catheter inserted through the vascular system of a patient to place the distal tip of the catheter in an artery feeding a selected organ of the patient. The '963 patent discloses a heat transfer bellows for cooling the blood flowing through the artery.
U.S. Pat. No. 6,767,346, issued to Damasco et al, entitled, “Cryosurgical Probe With Bellows Shaft”, discloses use of a cryosurgical probe with a bellows shaft. U.S. Pat. No. 6,936,045, issued to Yu et al, entitled, “Malleable Cryosurgical Probe” discloses a cryosurgical probe used for Joule-Thomson nozzles.
CryoCath Technologies, Inc., Montreal, Quebec, Canada, utilizes a cryoablation probe trademarked under the name Surgifrost® which involves the use of a cryoprobe with a malleable or corrugated shell. A problem with this and other similar products is that these cryoprobes are not sufficiently flexible for optimum use and still retain memory. As a result, there is often an incomplete/intermittent thermal contact along the whole line of freezing. The small contact area provides a limitation for the power delivered to the tissue.